Milling machines, and metal working machines in general, require precision tolerances to produce a quality work product. Machines such as Bridgeport milling machines have a machine head which holds a cutting head in a quill for use it machining metal which is attached to a milling table. The milling table of the Bridgeport milling machine is moveable, via a plurality of hand screws, so that the object being machined can be moved in relation to the cutting head. Additionally, this machine head is rotatable about one or two axes so that, for example, a flat bottomed cutting head can be used to machine a V groove in a piece of metal by rotating the machine head to an angle of 45.degree..
This ability to rotate the machine head in relation to the milling table, while convenient, causes several problems when the machine head must be realigned to its normal (or perpendicular) position in relation to the milling table. Since a milling machine is used to do high precision milling processes, it is imperative that this machine head and quill assembly be properly aligned with the milling table. There are currently several ways of aligning this machine head to the milling table, all of which are very cumbersome and/or require the use of expensive components.
Traditionally, a machine head is aligned to a milling table through the use of a precision bracket assembly and a dial indicator. The quill assembly of a milling machine is similar to that of a chuck on a drill press, where a bit is inserted into the quill assembly and it rotates about a predefined axis. A typical way of aligning a machine head/quill assembly to a milling table is to insert into the quill assembly an offset bracket which positions a dial indicator a predetermined distance away from the axis upon which the quill assembly turns. This offset is typically five (5) inches. In order to calibrate the milling table, the bracket is spun to a first position on the milling table (e.g. 90.degree.) and a reading is taken on the dial indicator. Then, the quill assembly (and the bracket) are rotated through a 180.degree. arc so that a second reading can be taken at a second position on the milling table (e.g. 270.degree.). Assuming that the milling table is in perfect alignment with the quill assembly along this first axis (the X axis), the readings on the dial indicator should be the same. In the event that there is any variation between the reading taken at 90.degree. and the reading taken at 270.degree., the machine head is out of alignment and must be aligned in relation to the X axis. This calibration procedure is repeated until the dial indicators read the same at the 90.degree. and 270.degree. intervals. Once this is completed, this calibration procedure is repeated for the Y axis, where readings are taken at 0.degree. and 180.degree. intervals.
Again, as with X axis calibration, the calibration procedures are repeated for the Y axis until the readings on the dial indicator are the same. At this point, the user must recheck the alignment along the X axis to verify that aligning the Y axis did not compromise the alignment of the X axis. Once this is done, the machine head is aligned in relation to the milling table and the milling process can begin. As can be imagined, this is a long and complicated process which can take a considerable amount of time to complete.
Alternatives to this procedure include a device which is essentially a large bell shaped object which is inserted into the quill assembly. This is a precision machined device which improves upon the idea of the rotatable dial indicator in that it measures in multiple axes simultaneously. To use this device, it is inserted into the quill assembly and then the user inserts feeler gauges between the lower surface of the bell and the milling table to determine the clearance between the bell and the table. If the quill is aligned in both axes (X and Y), the clearance measurements taken with the feeler gauges at points 0.degree., 90.degree., 180.degree. and 270.degree. would all be the same. While this simplifies the procedure of aligning the quill assembly with the milling table, this precision machined bell assembly is very large and requires essentially the use of the entire milling table to align the machine head. Additionally, this device is costly and requires considerable space to store.
Further, either of the two previously described devices can be utilized in conjunction with a sine plate. The use of a sine plate enables the above-mentioned devices to be used to position the milling head in non-perpendicular orientation in relation to the milling table. During use, a plurality of precision machined blocks are placed under one side of the sine plate so that the angle of the surface of the sine plate, in relation to the milling table, is the desired cutting angle. By varying the number of blocks utilized with the sine plate, the angle between the milling head and the milling table can be varied, allowing the milling head to be precisely positioned in relation to the milling table.